I. Field of the Invention
This disclosure relates generally to systems, apparatus and methods for position location of a mobile device, and more particularly to narrowing a list of access points based on a rough position, thereby more quickly detecting visible access points, which leads to a faster time-to-first position fix.
II. Background
Positioning support for location based on WiFi and Femtocell measurements by a mobile device 100 is defined in the OMA LPPe positioning protocol (e.g., other widely used positioning protocols like LPP, RRLP, RRC, IS-801 do not contain support for WiFi centric positioning and only allow Femtocell centric positioning without special enhancement). As background, reference is made to the following definitions, acronyms and abbreviations:
TABLE 13GPP3rd Generation Partnership ProjectADAssistance DataAPAccess PointIEEEInstitute of Electrical and ElectronicsEngineersLAIlocation area identifierLPPLTE Positioning ProtocolLTE3GPP Long Term EvolutionMSMobile StationOMAOpen Mobile AllianceOMA LPPeOMA LPP ExtensionsOWTOne-way TimeRFRadio FrequencyRSSIReceived Signal Strength IndicationRTTRound-trip TimeSLPService Location ProtocolSUPLSecure User Plane LocationUEUser EquipmentWiFi productany WLAN product based on the IEEE802.11 family of standardsWLANWireless Local Area Network
A problem with current support for WiFi and Femtocell centric positioning in LPPe is that assistance data (AD) for WiFi access points and Femtocells provides a potentially large number of access points in the assistance data. The large number of access points in the assistance data is not refined or filtered specific to a rough position of a particular mobile device. That is, the assistance data for the large number of access points is independent of which access points are more likely to be receivable or beneficial to positioning of the mobile device. For example, a large building or other structure (e.g., an office building, a shopping mall, an airport, a municipal center or an enterprise building) may contain a large number (e.g., hundreds) of access points that may be communicated to a mobile device via an assistance data message. In one example, a location server (e.g., a SUPL SLP) provides to the mobile device a large number of access points within an assistance data message.
Typically, at any location within a building or structure, a mobile device will only be able to receive and measure signals from some small fraction of this large number of access points. However, unless the mobile device 100 already has an accurate location estimate and can therefore determine (e.g., from provided access point (AP) location coordinates) which access points are nearest to it, it will not generally know which access points it will be able to detect and measure. Additionally, even when a mobile device does determine which access points are nearby, the presence of walls, floors and corridors in a building may mean that some nearby access points may not be detectable whereas other access points further away may be detectable due to good radio propagation conditions (e.g., such as that provided by an access point at the far end of a long corridor).
What is needed is a way to reduce a large access point list to a more relevant and shorter access point list for acquiring access point signals from which a position fix of a mobile device may be determined.